ModalAI Forum

it's more likely I will be commanding attitude / body rate which are already available

Indeed. I highly suggest you to use those two unless your application stricly requires direct actuation control.

I just wanted to get a clear overview of what the information dds client / agent can give me access to in the modalai version of px4.

By editing src/modules/microdds_client/dds_topics.yaml you can access any PX4 uorb message so the limit here is just about what has been implemented on PX4 that is or is not available in the voxl version.

How do you know what types of control / input & output data are not directly supported in px4 voxl version, as you said?

the type of offboard control you can achieve is exposed by OffboardControlMode.msg. As you can see in main PX4 you have

bool position
bool velocity
bool acceleration
bool attitude
bool body_rate
bool thrust_and_torque
bool direct_actuator

I've added thrust_and_torque and direct_actuator one year ago (more or less). However, latest voxl is still using the old version: this old version let's you control via thrust and torque setpoints but does not let you control the single motor individually.

Hi @jonathankampia , yes you can edit src/modules/microdds_client/dds_topics.yaml in PX4 and rebuilt it to add or remove topics.

I remember reading somewhere on this forum that the custom branched px4 firmware version may not support/provide some of the data

I'm don't know about that, it is easier to know which data from upstream PX4 you want and then check to see if it is available (after adjusting the bridge)

I am working on a project that will involve a VOXL 2 and may need to do direct actuator control

I guess you want /fmu/in/actuator_motors then. However, to use complete direct actuator control you will need to bring in some extra changes as direct actuator control is not supported in PX4 voxl version.

This is still better than going through the mavlink and mavros route because for direct actuation you probably want the lowest latency.

Actually, do you need to control a motor in direct mode or you need to control an auxiliary output (i.e. payload)? This makes a huge difference w.r.t. the topic and the workflow you need to use.

Hi, @voxl-phoenix ,

zenoh rmw is only available for ROS 2 humble, jazzy, and rolling. Foxy is too old and it is not supported (and I don't think it will ever be).

However, you can try https://github.com/eclipse-zenoh/zenoh-plugin-ros2dds if you want to use zenoh between PX4 and the companion computer while keeping the default ROS 2 DDS Middleware unchanged. The original PR that added Zenoh to PX4 should walk you trough the required steps: https://github.com/PX4/PX4-Autopilot/pull/22017
Note howevert that

• the original PR used https://github.com/eclipse-zenoh/zenoh-plugin-dds instead of the more recent zenoh-plugin-ros2dds.
• the latest zenoh version used in PX4 is quite different from the first one.

Therefore, use that more as a guideline, nothing more.

You also have

• https://github.com/PX4/PX4-Autopilot/pull/23462, which updated the PX4 zenoh version to 1.0.0
• https://github.com/PX4/PX4-Autopilot/pull/24476, the latest open PR that adds support to zenoh rmw

Please read through all of them carefully as they are the only source of PX4 doc for zenoh. Official PX4 doc will be published once the interface will exit the testing stage